1. Field of the Invention
This invention relates to a lamp unit for use in a heating treatment through light radiation to carry out some processing such as layer formation, diffusion, annealing or the like for a workpiece such as a semiconductor wafer and to a light radiation type heating device using this lamp unit. More particularly, the invention relates to a lamp unit capable of performing, for example, a high-speed heating process to form a shallow connecting surface at the annealing stage for the semiconductor wafer and to a light radiation heating device using this lamp unit.
2. Description of Related Art
In a semiconductor manufacturing stage, a light radiation heating device for performing a heating treatment with light containing a large amount of infrared rays radiated from filament lamps is used in order to perform processing such as layer formation, diffusion, annealing or the like. Although all these processes perform a heating operation for heating a semiconductor wafer up to a high temperature, application of a light radiation heating processing device enables the semiconductor wafer to be rapidly heated, and its temperature can be increased up to 1000.degree. C. or more within tens and several seconds to several tens seconds, for example. In addition, if the light radiation is stopped, the semiconductor wafer can be cooled rapidly.
FIG. 1 is a cross-sectional view of a prior art light radiation heating device. Filament lamps 4 to be described later are arranged in a lamp chamber 1 and a mirror 5 is installed at the rear surfaces of the filament lamps 4. A light radiation chamber 2 and a quartz window 9 define this lamp chamber 1. Within the light radiation chamber 2 a semiconductor wafer W is mounted which acts as a workpiece that is heated and processed on a wafer holding block 3. In addition, the quartz window 9 is used in case the atmosphere near the semiconductor wafer W is different from the atmosphere in the lamp chamber 1.
One example of a filament lamp 4 is illustrated in FIG. 2, wherein a seal member for the filament lamp 4 includes an annular light emitting tube 7, a pair of inlet tubes 8 which are cooperatively arranged at a right angle to the end of the light emitting tube 7, and a filament 12 having a tungsten raw wire wound in a helical form installed within the light emitting tube 7. A seal section 11 is formed at the end part of each inlet tube 8. The end of the filament 12 and the lead wire 19 are connected at the seal section 11 through a molybdenum foil 11a. Within the sealed member is enclosed a small amount of halogen gas together with inert gas.
As shown in FIG. 3, the annular light emitting tubes 7 of the filament lamp 4 are constructed such that the light emitting tubes 7 of semi-circular or divided circle or arcuate shape are combined to form a circular shape.
In FIG. 1, the light emitting tubes 7 are of circular shape, and a plurality of filament lamps 4 having different diameters D are arranged such that the light emitting tubes 7 are installed in a concentric manner around a center X of the circle. The mirror 5 arranged at the rear surfaces of the filament lamps 4 is made of metal, for example, aluminum, and there are provided some concentric grooves 13 covering the light emitting tubes 7 of the filament lamps 4 and through-pass holes 6 into which the inlet tubes 8 are inserted. The reflecting surface of the mirror 5 is provided with metallic plating, such as a gold plating, so as to attain an improved reflection of light. The light emitting tube 7 of each of the filament lamps 4 is arranged and fitted in the concentric grooves of the mirror 5. In addition, the inlet tube 8 of each of the filament lamps 4 is inserted into the through-pass hole 6 of the mirror 5 and protrudes from the rear surface of the mirror 5.
Accordingly, as electrical power is fed to the filament lamps 4, a filament 12 may produce and radiate light. The light is reflected at the mirror 5 and radiated against the semiconductor wafer W on the wafer holding block 3 within the light-radiating chamber 2.
In recent years, it has become necessary to attain a high integrated formation and ultra fine arrangement of a semiconductor integrated circuit, wherein it has been most important to make a thin diffusion layer containing some impurities and to form a shallow junction surface during a stage in which the impurities are implanted into and diffused in the silicon crystal in the semiconductor wafer, for example through an ion implanting process. Although the diffusion of impurities performed through the ion implanting process is carried out at an implanting stage in which the ionized impurities are accelerated with an electric field and physically implanted into the silicon crystal and also at an annealing stage in which the impurities are diffused in the crystal while the damage of the crystal through implanting of impurities is being recovered, it is necessary to restrict the diffusion of impurities to attain a thin diffusion layer at an annealing stage in order to form a shallow junction surface and further in order to obtain a thin diffusion layer by making the temperature increasing speed of the semiconductor wafer high. If the temperature increasing speed is slow, the annealing processing time is extended, the diffusion of the impurities exceeds a predetermined diffusion layer thickness and the layer becomes too thick. In turn, if the layer thickness of the diffusion layer is required to have 0.13 to 0.15 .mu.m, for example, it becomes necessary to have a temperature increasing speed of 150 to 200.degree. C./sec.
However, in the case of the prior art light radiation heating device, the temperature increasing speed of the semiconductor wafer was approximately 50 to 100.degree. C./sec. Accordingly, due to the recent years request of a higher integration and more fine formation of the semiconductor integrated circuit, the annealing stage for the diffusion of impurities by an ion implanting process cannot accommodate for the requirement of making thin diffusion layers of impurities and of forming a shallow junction surface.